The present invention relates to method and apparatus for treating the surface of a semiconductor and, more particularly, the invention relates to a surface treating method and apparatus for etching the surface of a semiconductor using a plasma.
Hitherto, for treating the surface of a semiconductor, a plasma etcher for etching a semiconductor in a plasma has been used. Conventional techniques will be described by using an etcher, called an ECR (electron cyclotron resonance) etcher, as an example. According to the ECR etcher, a plasma is generated by microwaves within a chamber to which a magnetic field is applied from the outside. The motion of electrons is circular around the magnetic field, and high density plasma is produced by resonance of electron motion and the microwaves. In order to accelerate ions impinging on a sample, such as a semiconductor, a high frequency voltage is applied to the sample. A halogen gas formed from chlorine, fluorine, or the like is used as a plasma gas.
Among conventional etchers of this kind, an etcher for realizing high accuracy during processing is disclosed in Publication of Unexamined Japanese Patent Application (JP-A) No. 6-151360 (corresponding to U.S. Pat. No. 5,352,324). According to this technology, by on-off modulating a high frequency voltage to be applied to the sample, the selectivity between silicon (Si) serving as a substance to be etched and an underlying oxide film can be increased and the aspect ratio dependence can be reduced. JP-A-8-339989 (corresponding to U.S. Pat. No. 5,614,060) discloses a method which can reduce etch residue by overlapping short pulses of a continuous rf bias power in etching performed on a metal. JP-A-62-154734 discloses a method of processing a taper by introducing a gas capable of bringing about deposition and etching and alternately applying a DC bias which is higher than a predetermined potential and a DC bias which is lower than the predetermined potential. JP-A-60-50923 (corresponding to U.S. Pat. No. 4,579,623) discloses a method of improving the surface treating characteristics by periodically varying the amount of etching gas being introduced and also by changing the time of application of the high frequency voltage. Examined Japanese Patent Application Publication No. 4-69415 (corresponding to U.S. Pat. No. 4,808,258) discloses a method of improving the etch characteristic by modulating the high frequency voltage to be applied to a sample. Further, U.S. Pat. No. 4,585,516 discloses a method of improving the uniformity in the etch rate in the plane of a wafer by modulating the high frequency voltage of at least one of high frequency power supplies connected to two electrodes in a triode etcher.
As the integration of a semiconductor becomes finer, the processing dimension between a line corresponding to a conductive line or an electrode and a space enters a region of 1 μm or smaller, preferably, 0.5 μm or smaller. In the processing of such a fine pattern, a problem occurs in that lines gradually become thicker and a pattern cannot be formed according to a design dimension. Further, in addition to an aspect ratio dependent etch rate, an aspect ratio dependent etch profile becomes conspicuous, thereby hindering the processing.
Moreover, the thickness of a gate oxide film of a MOS (metal oxide semiconductor) transistor is equal to or smaller than 6 nm in a 256 Mbit or larger LSI (Large Scale Integration). In such devices, the degree of anisotropy and the selectivity between a material to be etched and the underlying oxide film have the relation of a trade-off, so that the processing is made more difficult.
Many of the conventional techniques were developed when the minimum feature size of a device was 1 μm or larger. It is becoming difficult to use these techniques to process a device of finer scale. In processing such a fine scale device, it is necessary to set accurate process parameters based on an analysis of the relation between plasma parameters and etch characteristics. At present, many manufactures expend a considerable effort on this determination. By such an organized process, a new device which is qualitatively different also can be processed.